Climate Change Research Since World War II

With the dawn of the nuclear age at the end of World War II, atmospheric and oceanic scientists became preoccupied with other products of human ingenuity, namely radioactive wastes. Anxiety was escalating. Would radioactive carbon dioxide (14CO2), which was generated in the atmosphere during nuclear explosions, dissolve in the oceans and widely contaminate sea life and seafood?

Roger Revelle (1909–1991) and Hans Suess (1909–1993) of the Scripps Institution of Oceanography in San Diego, California, analyzed the exchange of 14CO2 between the atmosphere and the oceans. They published a seminal work in 1957 showing that only a thin, upper layer of seawater rapidly exchanged materials with the atmosphere. [1] These results had broad implications. On the positive side, contamination of sea life from nuclear testing would be highly localized; but on the negative side, the oceans would remove only a small portion of the 14CO2 being released into the atmosphere; most of the radioactive gas would remain airborne. By analogy, these results indicated that only a small portion of the CO2 released from fossil-fuel burning would dissolve in the oceans: the bulk would remain in the atmosphere, and atmospheric CO2 concentrations would increase substantially.

By the mid-1950s, technological advances had increased the precision of CO2 measurements tenfold. C. D. (Dave) Keeling (1928–2005), also of Scripps, obtained funds sufficient to equip two weather stations with instruments that monitored atmospheric CO2 with unprecedented accuracy. To minimize the influence of local disturbances, he chose sites that were remote from industrial and biological sources of CO2 and were subject to strong prevailing winds. One site was at the South Pole and the other was on the Island of Hawaii, at the Mauna Loa Observatory atop the northern flank of the Mauna Loa volcano, at an elevation of 3,397 meters.

Monitoring at the South Pole began in September 1957 and at Mauna Loa six months later. Concentrations of CO2 at the South Pole rose slowly, but steadily. The CO2 measurements at Mauna Loa, however, oscillated from month to month, raising doubts about whether this instrument was performing properly. [2] Fortunately, with more observations, Keeling realized that the oscillations at Mauna Loa reflected the annual cycle on nearby continents of relatively rapid plant growth in summer, which removes CO2 from the atmosphere, and relatively rapid biological respiration in winter, which releases CO2 to the atmosphere. Funding for the South Pole station ran out after about 2 years, during which time data showed a rise in CO2 concentrations from 311 ppm to 314 ppm (parts per million; 1 ppm = 0.0001%). The Mauna Loa station has provided a nearly continuous record of rising atmospheric CO2 concentrations from about 315 ppm in 1957 to about 385 ppm in 2007, an increase of about 20%. This record has become known as the Keeling curve.

As evidence accumulated, the scientific establishment became more receptive to the idea of global warming and its relationship to atmospheric CO2 concentrations.

[1] Revelle, R. and H. E. Suess (1957) Carbon dioxide exchange between atmosphere and ocean and the question of an increase of atmospheric CO2 during the past decades. Tellus 9:18-27.